Method and apparatus for making a lid with an optically transmissive window

ABSTRACT

A metal plate ( 126 ) has a plurality of openings ( 127 ) extending through it, and is cleaned using a wet hydrogen process ( 157 ). Glass windows ( 106 ) are then placed in the openings, and are each fused to the metal plate by heat ( 231 ) in a manner so that each window projects outwardly on each side of the plate. Both sides of each window are then simultaneously ground and polished ( 232 ). Exposed surfaces of the metal plate are electroplated with nickel and gold ( 236 ). One or more coatings ( 41, 46, 47 ) are applied to one or both sides of each window. Several sections are then cut from the assembly, each of which can serve as a lid ( 17 ) for an optical apparatus ( 10 ).

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional application of U.S. patentapplication Serial No. 10/045,639, filed Nov. 6, 2001 and entitled“Method and Apparatus for Making a Lid With an Optically TransmissiveWindow,” now U.S. Pat. No. 6,745,449 issued Jun. 8, 2004.

TECHNICAL FIELD OF THE INVENTION

[0002] This invention relates in general to a lid having a frame whichsupports a window transmissive to radiation and, more particularly, to amethod and apparatus for fabricating such a lid.

BACKGROUND OF THE INVENTION

[0003] An existing device includes a housing with an opening thereinwhich is closed by a lid. The lid includes a frame, and a window whichis disposed within and hermetically sealed to the frame, the windowbeing transmissive to radiation in a waveband of interest. The devicecan be used in a television or a projector to form images, which aretypically projected onto some type of screen so that they can be viewedby a person. The device includes within the housing a digitalmicromirror device (DMD) of a known type. A beam of radiation enters thehousing through the window in the lid, is processed by the digitalmicromirror device to form a plurality of sub-beams which represent animage, and at least some of the sub-beams then exit the housing throughthe window in order to facilitate the generation of the image, which isprojected onto the screen.

[0004] This existing lid is made by forming a metal frame which has anopening through it, placing a piece of glass in the opening through theframe, and then heating the frame and glass until the peripheral edgesof the glass become fused to the edges of the opening in the frame. Theside surfaces of the glass are then ground and polished, and one or morecoatings are applied to both sides of the glass. While this existing lidand the process of making it have been generally adequate for theirintended purposes, they have not been satisfactory in all respects.

[0005] In this regard, different applications require lids of variousdifferent sizes, and/or glass windows of various different sizes.Fabricating each lid as a separate part is time-consuming and expensive,due in part to the separate handling and processing needed for each lid,and also due in part to the fact that separate tooling is needed foreach different frame size, and the separate tooling is relativelyexpensive. In this regard, grinding and polishing of the opposite sidesurfaces of the glass window in each separate frame requires a specialsupport part capable of properly supporting a frame of that size withina double-disk grinding apparatus, and each such support part must beconfigured to conform to the particular size of the lid. Some lidconfigurations are not associated with a high-volume market, and hightooling costs can thus represent a significant portion of the overallmanufacturing cost of each individual lid.

[0006] A different consideration is that, when fusing each piece ofglass to the associated frame, impurities in the frame can cause theformation of gases. For example, carbon impurities in the frame can leadto the formation of carbon-based gases. Since the glass is softened bythe heat used for fusing, the gases can in turn produce bubbles withinthe glass. An excessive quantity of bubbles can degrade the opticalproperties of the glass window to an extent where the lid is considereddefective and must be discarded. This obviously reduces the effectiveyield of the fabrication process. Techniques have been developed toclean metal frames by removing impurities, for example by processing theframes in a disassociated ammonia environment. However, these techniqueshave not been satisfactory in all respects. In particular, thesetechniques have helped to reduce the number of impurities and thus thenumber of gas bubbles in the glass, thereby increasing productionyields. But the number of parts which must be discarded as defective isstill undesirably high, which in turn causes the cost of thesatisfactory lids to be undesirably high.

SUMMARY OF THE INVENTION

[0007] According to a first form of the present invention, a method isprovided and involves: forming a plurality of windows which are eachtransmissive to radiation having a predetermined wavelength; fabricatinga plate with a plurality of openings therethrough; fixedly securing eachwindow to the plate in a manner so that an annular seal is providedbetween an annular portion of the window extending along a peripherythereof and an annular portion of the plate extending around theopening; simultaneously processing a respective surface on each of thewindows secured to the plate; and thereafter cutting from the plate aplurality of sections which each include a respective one of the windowsand a respective one of the annular portions of the plate.

[0008] According to a different form of the invention, an apparatusincludes: a plate having a plurality of openings therethrough; and aplurality of windows which are each transmissive to radiation having apredetermined wavelength, each window being secured to the plate in amanner providing an annular seal between an annular portion of thewindow extending along a periphery thereof and an annular portion of theplate extending around the opening, and each window having thereon asurface which needs to be processed.

[0009] According to still another form of the invention, a methodinvolves: heating a metal part in a wet hydrogen atmosphere; thereafteroxidizing a surface of the metal part; thereafter placing a glass partin contact with the surface of the metal part; and thereafter heatingthe metal part and the glass part to cause the glass part to becomefused directly to the metal part.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] A better understanding of the present invention will be realizedfrom the detailed description which follows, taken in conjunction withaccompanying drawings, in which:

[0011]FIG. 1 is a diagrammatic sectional side view of an apparatus whichincludes a housing with an opening closed by a lid embodying the aspectsof the present invention;

[0012]FIG. 2 is a diagrammatic exploded perspective view of the lid ofFIG. 1;

[0013]FIG. 3 is a diagrammatic sectional side view of a portion of thelid of FIG. 1;

[0014]FIG. 4 is a flowchart showing a sequence of steps that are carriedout to make glass windows in a method which embodies aspects of thepresent invention;

[0015]FIG. 5 is a diagrammatic perspective view of a glass windowproduced by the method of FIG. 4;

[0016]FIG. 6 is a flowchart showing a sequence of steps that are carriedout to make a metal plate in a method which embodies aspects of thepresent invention;

[0017]FIG. 7 is a diagrammatic bottom view of a metal plate produced bythe method of FIG. 6;

[0018]FIG. 8 is a diagrammatic top view of the metal plate of FIG. 7;

[0019]FIG. 9 is a diagrammatic fragmentary sectional side view takenalong the line 9-9 in FIG. 8;

[0020]FIG. 10 is a flowchart showing a sequence of steps that arecarried out to assemble various parts in a method which embodies aspectsof the present invention;

[0021]FIG. 11 is a diagrammatic top view of a lower fuse plate which ispart of some tooling used during the method of FIG. 10;

[0022]FIG. 12 is a diagrammatic sectional side view taken along the line12-12 in FIG. 11;

[0023]FIG. 13 is a diagrammatic top view of an upper fuse plate which ispart of the tooling used during the method of FIG. 10;

[0024]FIG. 14 is a diagrammatic sectional side view taken along the line14-14 in FIG. 13;

[0025]FIG. 15 is a diagrammatic perspective view of a counterweightwhich is part of the tooling used in the method of FIG. 10;

[0026]FIG. 16 is a diagrammatic sectional side view of an assembly whichexists at an interim stage of the method of FIG. 10; and

[0027]FIG. 17 is a diagrammatic top view of a further assembly whichexists at an interim stage of the method of FIG. 10.

DETAILED DESCRIPTION OF THE INVENTION

[0028]FIG. 1 is a diagrammatic sectional side view of an apparatus 10which embodies aspects of the present invention. The apparatus 10includes a housing 11 which has a chamber 12 therein, and which has atop wall with a vertical opening 13 through it. A digital micromirrordevice (DMD) 16 of a known type is supported within the chamber 12, inthe center of the top surface of the bottom wall of the housing 11. TheDMD 16 has on an upper side thereof a two-dimensional array of tinyreflective mirrors. These mirrors each correspond to a respective pixelof an image, and can each be independently physically moved by the DMD16 in response to electrical control signals.

[0029] A lid 17 is provided on top of the housing 12, so as to close theopening 13 in a manner effecting a hermetic seal between the interiorand exterior of the housing 11. In this regard, the peripheral edges ofthe lid 17 are seam welded in a known manner to the top surface of thehousing 11. A gas is provided in the region 18 within the chamber 12,and the lid 17 ensures that this gas does not escape from the region 18in the chamber 12. The gas serves to lubricate the mirrors of thetwo-dimensional array on the DMD 16, in order to facilitate theirmovement, and to ensure that they have a relatively long operationallifetime. However, this gas is also somewhat corrosive, and the housing11 and lid 17 are thus resistant to corrosive damage from the gas.

[0030]FIG. 2 is a diagrammatic perspective exploded view of the lid 17.With reference to FIGS. 1 and 2, the lid 17 includes an annular metalframe 23, and a window 24 which is fixedly mounted within the frame. Inthe disclosed embodiment, the frame 23 is made from a steel material,for example the type of material which is readily commercially availablefrom a number of different vendors as ASTM-F15. The frame 23 is aplate-like element with parallel top and bottom surfaces, the outer edgeof the frame 23 having an approximately rectangular shape. An opening 27extends vertically through the center of the frame 23. The opening 27has a shape which is approximately rectangular, except that it hasrounded corners. The frame 23 has in its upper side an annular groove orrecess 29 of approximately rectangular cross section. This recess 29extends along the entire peripheral edge of the frame, so as to definealong the entire periphery of the frame an outwardly projecting annularflange 32 which has a generally uniform width and thickness.

[0031] The window 24 is a plate-like element having parallel top andbottom surfaces, and has approximately the same thickness as the frame23. The outer edge of the window has the shape of a rectangle withrounded corners, and in fact the window 24 has approximately the samesize and shape as the opening 27 through the frame 23. The peripheraledge of the window 24 is fused directly to the material of the frame 23along the entire length thereof, thereby defining an annular sealbetween the window 24 and frame 23 which extends completely around thewindow 24. This is a hermetic seal, which helps to keep the corrosivegas within the region 18 in the chamber 12 of the housing 11. Thetechnique used to fuse the edges of the window 24 to the frame 23 isdiscussed in more detail later.

[0032] The window 24 includes a layer 38 of a borosilicon glassmaterial, which in the disclosed embodiment is commercially available ascatalog number 7056 from Corning Incorporated of Danville, Va. Thisparticular glass material is transmissive to radiation in a range whichis centered at a wavelength at about 545 nm, and which extends fromapproximately 420 nm to about 700 nm. Further, this particular glassmaterial has an index of refraction which is approximately 1.47 to 1.50for radiation at the center wavelength of 545 nm. However, it wouldalternatively be possible to use a different glass material which istransmissive to radiation in a different range of wavelengths, and/orwhich has a different index of refraction for radiation within the rangeof interest.

[0033] The window 24 has, on the underside of the glass layer 38, a verythin layer 41 of an opaque material, which in the disclosed embodimentis chrome. For clarity the thickness of the chrome layer 41 isexaggerated in the drawings in relation to the sizes of other parts. Arectangular aperture 42 is provided through the center of the chromelayer 41. The chrome layer 41 may optionally be omitted from the window24.

[0034] The window 24 further includes, on both the top and bottom sidesthereof, a very thin coating of an antireflective (AR) material. Forclarity, the AR coatings are not separately shown in FIGS. 1 and 2.However, FIG. 3 is a diagrammatic fragmentary sectional side view of asmall portion of the window 24, and shows the glass layer 38, the chromelayer 41 with the aperture 42, and also the AR coatings at 46 and 47.For clarity, the thicknesses of the chrome layer 41 and the AR coatings46-47 are all exaggerated in FIG. 3. The AR coatings 46 and 47 are eachtransmissive to radiation within the above-mentioned range ofapproximately 420 nm to about 700 nm. In the disclosed embodiment, theAR coatings 46-47 are both made from silicon dioxide. However, theycould alternatively be made from some other suitable anti-reflectivematerial, such as magnesium fluoride.

[0035] With reference to FIG. 1, the apparatus 10 operates as follows. Abeam of inbound radiation, which is represented diagrammatically by twoarrows 56 in FIG. 1, passes through the window 24 and travels to the DMD16. Each of the mirrors of the DMD 16 reflects a respective portion ofthe beam in a respective direction determined by the current physicallocation of that mirror. The various independently reflected portions ofthe original beam are each referred to here as a sub-beam. The differentsub-beams then travel away from the DMD 16 in various differentdirections, and at least some of them will travel back out through thewindow 24, as indicated diagrammatically in FIG. 1 by two arrows 57.

[0036] For simplicity, the arrows representing the inbound radiation 56and the outbound radiation 57 are shown as vertical lines in FIG. 1, butit will be recognized that various different beams and sub-beams wouldtypically be traveling in various different directions. All of theradiation 56-57 passing in either direction through the window 24 must,of course, pass through the aperture 42 in the chrome layer 41.

[0037] A method for simultaneously making several of the lids 17 willnow be described. FIG. 4 is a flowchart showing a portion of thismethod. In particular, FIG. 4 shows a sequence of steps which arecarried out to make a plurality of glass elements that will each becomea glass layer 38 within the window 24 of a respective lid 17. In moredetail, block 101 in FIG. 4 indicates that raw glass material is shapedinto a plate. As noted above, the raw glass material used in thedisclosed embodiment is a borosilicate glass material which iscommercially available as catalog number 7056 from Corning Incorporated.A quantity of this raw glass material is heated for approximately 16hours at a temperature which is increased progressively from an ambientroom temperature of about 25° C. to a temperature of 1050° C. Thisheated glass material is then pressed and/or formed into a sheet havinga uniform thickness of about 0.155 inches. This glass sheet is thengradually cooled back to 25° C.

[0038] Next, at block 102, the glass sheet is cut into a plurality ofseparate glass window elements. FIG. 5 is a diagrammatic perspectiveview showing one of these glass window elements at 106. The glass windowelements 106 are each cut from the glass sheet by machining or milling,or by using a laser. The peripheral edge of the glass window 106 has anapproximately rectangular shape, with rounded corners, so that theelement 106 has effectively the same size and shape as the opening 27(FIG. 2) in one of the frames 23. The glass window 106 is at this pointsomewhat thicker than the glass layer shown at 38 in FIGS. 2 and 3,because a portion of the glass window 106 will be subsequently removedby grinding and polishing, as discussed later.

[0039]FIG. 6 is a flowchart showing a sequence of steps which arecarried out to make a metal plate having several sections that eachcorrespond to the frame 23 of FIG. 2. The sequence shown in FIG. 6begins with a sheet of raw metal which, in the disclosed embodiment, isa steel material commercially available as ASTM-F15. As indicted atblock 121 in FIG. 6, this sheet of metal is subjected to fine-blanking,in order to create from it one or more square metal plates which, in thedisclosed embodiment, each have a size of 7 inches by 7 inches. Thefine-blanking process simultaneously creates a two-dimensional array ofopenings through each plate, where each opening is approximatelyrectangular but has rounded corners. In this regard, FIG. 7 is adiagrammatic bottom view of a square metal plate 126 which is one of the7 inch by 7 inch plates separated from the metal sheet by fine-blanking.The plate 126 has twenty of the approximately rectangular openings 127extending through it. These openings 127 are arranged in an array havingfive rows and four columns.

[0040] Next, as indicated at block 122 in FIG. 6, the plate 126 issubjected to double-disk grinding of a known type, in order to give it aselected uniform thickness, which in the disclosed embodiment is 0.115inches. Then, with reference to block 131 in FIG. 6, twenty annulargrooves are machined into an upper side of the plate 126. In thisregard, FIG. 8 is a diagrammatic top view of the plate 126, showing theannular grooves 136. FIG. 9 is a diagrammatic fragmentary sectional sideview of a portion of the plate 126, taken along the section line 9-9 inFIG. 8. It will be noted that each of the annular grooves 136 extendsaround one of the respective openings 127, in a manner so that thegroove 136 is spaced outwardly a small distance from the opening 127along the entire periphery of the opening 127.

[0041] Adjacent grooves 136 are spaced a small distance from each other,thereby defining a grid of perpendicular ribs 142 and 143 which eachhave the same vertical thickness as the plate 126, and which serve torigidify the central region of the plate 126 during subsequentprocessing. The plate 126 will eventually be cut up to form 20 frameswhich are each equivalent to the frame 23 (FIGS. 1-2), in a mannerdiscussed in more detail later.

[0042] Next, and still referring to block 131 in FIG. 6, severalalignment holes of various sizes and shapes are machined or drilledthrough the plate 126. Examples of these alignment holes are indicatedby reference numerals 137-139 in FIGS. 7-8. At block 146 in FIG. 6, theplate 126 is deburred using known techniques. Then, at block 147, theplate 126 and several other similar plates are loaded into a suitablesupport rack, and are rinsed in de-ionized (DI) water.

[0043] Then, with reference to block 148, the support rack with theplates thereon is immersed into a surfactant solution (soap solution)having a temperature of approximately 50° C. to 75° C., for a timeinterval in the range of approximately 5 minutes to 15 minutes. The rackand plates are then removed from this solution. Next, at block 151, therack and the plates are rinsed with de-ionized water at roomtemperature.

[0044] Then, at block 152, the plates are etched by immersing the rackand plates into a room temperature ferric chloride solution for a timeinterval in the range of approximately 1 minute to 4 minutes. The rackand plates are then removed from this solution, and are allowed todrain. Then, at block 153, the rack and plates are rinsed for 15 minuteswith room temperature de-ionized water. Then, at block 156, the rack andplates are dried at 150° C. for 20 minutes.

[0045] Next, the plates 126 are transferred from the rack to a ceramicsupport member, and are processed in a wet hydrogen furnace with a dewpoint setting of 15 to 30 PPM/° C. for a time interval in the range ofapproximately 11 to 15 minutes, while maintaining a peak temperature ofapproximately 950° C. to 1100° C. This serves to clean the metal platesby removing carbon, oxygen and sulfur impurities from the plates, alongwith other trapped contaminates, through the formation of products suchas CH₄, CO₂ and CO+H₂.

[0046] As an alternative to the wet hydrogen process discussed above inassociation with block 157, the plates and the ceramic support membercould be subjected to a 3:1 disassociated ammonia atmosphere with a dewpoint setting of 20 to 40 PPM/° C. for a dwell time of 10 to 30 minutes,while maintaining a temperature of approximately 1000° C. to 1250° C.

[0047] After completion of the wet hydrogen process discussed inassociation with block 157, the method proceeds to block 158, where theplates are transferred to a different ceramic support member. The platesare then oxidized by placing the plates and the ceramic support memberin a wet nitrogen furnace for a time interval of approximately 9 to 13minutes, while maintaining a peak temperature of approximately 600° C.to 1000° C. The layer of oxidation formed on the frames by this wetnitrogen process will have a thickness in the range of approximately 3 Åto 10 Å, and helps to increase the strength of the bond which will beformed between the glass and the metal. Too little oxidation or too muchoxidation can serve to weaken the bond.

[0048]FIG. 10 is a flowchart which shows a sequence of steps that arecarried out in the disclosed embodiment in order to assemble the plate126 (FIGS. 7-9) with 20 glass windows of the type shown at 106 (FIG. 5).In block 201, a sample subset of the metal plates 126 is selected forinspection, and a sample subset of the glass windows 106 is selected forinspection. In the disclosed embodiment, the inspection of frames andwindows is carried out so as to obtain a 1% acceptable quality level(AQL), which is an industry standard technique where a table is used todetermine the number of parts that need to be inspected in order toassure a specified quality level. The following explanation of theassembly procedure deals with plates and windows which have passed theinspection procedure.

[0049] In block 202 of FIG. 10, each of the glass windows 106 is cleanedby etching it in a 49% hydrofluoric acid solution for 30 seconds to 2minutes at 20° C. to 40° C. Then, each glass window 106 is rinsed inde-ionized water. Thereafter, each glass window 106 is baked until it isthoroughly dry, for example at a temperature of 150° C. for 20 minutes.

[0050] Next, with reference to block 203 in FIG. 10, the plate 126 andtwenty of the windows 106 are assembled through the use of fuse tooling,which holds them in proper position with respect to each other untilthey can be fused together. In this regard, FIG. 11 is a diagrammatictop view of a lower fuse plate 207, which is part of the reusable fusetooling provided for assembly. FIG. 12 is a diagrammatic sectional viewof the lower fuse plate 207, taken along the section line 12-12 in FIG.11. The plate 207 is made of a graphite material, has a size of 7 inchesby 7 inches, and has in an upper side thereof a plurality of shallowrecesses 208. The recesses 208 are each approximately rectangular withrounded corners, so as to have approximately the same size and shape asthe window elements 106.

[0051]FIG. 13 is a diagrammatic top view of an upper fuse plate 211,which is a further part of the reusable fuse tooling. FIG. 14 is adiagrammatic sectional side view of the fuse plate 211, taken along theline 14-14 in FIG. 13. The fuse plate 211 is made of a graphitematerial, has a size of 7 inches by 7 inches, and has a plurality ofopenings 212 extending through it. Each of the openings 212 has anapproximately rectangular shape with rounded corners, and the size andshape of the openings 212 correspond to the size and shape of the windowelements 106.

[0052]FIG. 15 is a diagrammatic perspective view of a counterweight 216,which is a further component of the reusable fuse tooling. Thecounterweight 216 is a plate-like element having parallel top and bottomsurfaces, and having a peripheral edge which is shaped to beapproximately rectangular with rounded corners. The counterweight ismade of a graphite material, and the length and width of thecounterweight 216 are slightly less than the length and width of each ofthe glass windows 106.

[0053]FIG. 16 is a diagrammatic sectional side view of an assembly 221which includes the lower fuse plate 207, the upper fuse plate 211, themetal plate 126, twenty of the glass windows 106, and twenty of thecounterweights 216. In more detail, twenty of the glass windows 106 areeach placed on the lower fuse plate 207 so that a lower portion thereofis disposed in a respective one of the shallow recesses 208. The metalplate 126 is then added, by moving it in a downward direction until itis rests on top of the lower fuse plate 207. The twenty glass windows106 will each be received within a respective opening 127 in the metalplate 126. The glass windows 106 each have an initial thickness which issomewhat larger than the thickness of the metal plate 126. The shallowrecesses 208 each have a depth which is approximately half of thedifference between the thickness of the glass windows 106 and thethickness of the metal plate 126. Consequently, as evident from FIG. 16,the recesses 208 position the window elements 106 so that each windowelement 106 projects outwardly by approximately the same amount on eachside of the plate 126.

[0054] Next, the upper fuse plate 211 is added to the assembly, bymoving it downwardly until it is resting on top of the metal plate 126.The upper portion of each of the glass windows 106 is received withinthe lower portion of a respective opening 212 through the upper fuseplate 211. Then, a respective one of the counterweights 216 is placed ontop of each of the glass windows 106. The counterweights 216 serve tohold the glass windows 106 in place while the glass is being fused tothe metal plate 126, which occurs in a manner discussed below. Thecounterweights 216 are sized so that they have sufficient weight to holdthe glass windows 106 in place, but without exerting so much force thatthe material of the glass windows 106 will tend to flow and deform whenheated during the fusing process.

[0055] Next, referring to block 231 in FIG. 10, the assembly 221 isplaced in a furnace and fired in an inert atmosphere at a temperature of900° C. to 1050° C. The assembly 221 is in the furnace for a time periodfrom 1 hour and 45 minutes to 2 hours and 15 minutes, and is at the peaktemperature for approximately 20 minutes. At this temperature, thematerial of the glass windows 106 softens, and the peripheral edge ofeach glass window 106 becomes directly fused to the edge of theassociated opening 127 through the metal plate 126, all along thecircumference thereof. At the end of the specified time interval, theassembly 221 is allowed to cool back to room temperature, so that theglass windows 106 harden again and become fixedly bonded to the metalplate 126. This creates a hermetic seal between the glass windows 106and the metal plate 126 along the entire peripheral edge of each of theglass windows 106.

[0056] Due to the fact that the metal plate 126 has been cleaned throughuse of the wet hydrogen procedure discussed above (block 157 in FIG. 6),carbon and other impurities in the metal are substantially reduced,which in turn reduces the extent to which these impurities may producevarious gases during the fusing process, which in turn substantiallyreduces the extent to which such gases can create undesirable bubbleswithin the material of the glass windows 106.

[0057] When the fusing process is complete, the metal plate 126 and theglass windows 106 secured thereto are separated from the fusing tooling,including the counterweights 216 and the upper and lower fuse plates 207and 211. Due to the fact that the fuse plates 207 and 211, and thecounterweight 216, are made from a graphite material, the glass material106 does not tend to fuse to them during the fusing process, and it isthus not difficult to separate the metal plate 126 and glass windows 106from the fuse tooling.

[0058] Due to the fact that the glass material of the windows 106reaches a melting temperature and softens during the fusing process, thesurfaces on opposite of each glass window 106 typically have theiroptical properties affected by the fusing process. Therefore, withreference to block 232 in FIG. 10, the opposite side surfaces of eachglass window 106 are subjected to grinding and polishing. The separateterms “grinding” and “polishing” are both used herein, because it iscustomary in the industry to use both terms. But it will be recognizedthat grinding and polishing both involve abrasive refinement of thesurfaces of the windows 106, and basically differ only in regard to thecoarseness of the abrasive media which is utilized.

[0059] In the disclosed embodiment, both sides of all 20 glass windows106 are ground and polished simultaneously. This is carried out throughuse of a not-illustrated double-disk grinding arrangement of a knowntype. In this double-disk grinding arrangement, two abrasive and coaxialdisks with diameters of about 24 inches are rotated relative to eachother, and the metal plate 126 with the glass windows 106 securedtherein is placed between two facing surfaces on the disks, so that theopposite sides of each glass window 106 each engage a respective surfaceon a respective disk. Both side surfaces of each of the glass windows106 are then ground and polished simultaneously, until each side surfaceis approximately flush with either the top surface or the bottom surfaceof the metal plate 126.

[0060] This grinding and polishing is carried out so as to achievespecified optical criteria. In the disclosed embodiment, the opticalcriteria are that both the top and bottom surfaces of each glass window106 are polished to a flatness of four fringes spherical power and twofringes irregularity. Simultaneous grinding and polishing of both sidesof all of the glass windows 106 provides a significant cost reductionover pre-existing techniques, where grinding and polishing are carriedout on a single glass window mounted in a single metal frame.

[0061] Referring to block 233 in FIG. 10, when the grinding andpolishing has been completed so as to meet the specified opticalcriteria, the assembly which includes the metal plate 126 with thewindows 106 is subjected to processing which cleans the exposed surfacesof the metal plate 126. In particular, the assembly which includes themetal plate 126 and the glass windows 106 is successively immersed in anacid descale bath, an alkaline clean bath, and a hydrochloric acid bath.These baths serve to clean the exposed surfaces of the metal plate 126in preparation for plating, including removal of the oxidation which wasformed on the metal in block 158 of FIG. 6. In this regard, the purposeof the oxidation was to provide a surface on the metal plate 126 whichwould ensure a secure bond between the metal plate 126 and the glasswindows 106. As to other surface portions of the metal, which are notengaged by the glass, it is appropriate to remove the oxidation fromthese surfaces so that these surfaces can be plated.

[0062] Next, at block 236, the exposed surfaces of the metal plate 126are electroplated with a layer of nickel having a thickness of at least200 microinches. Then, a layer of gold is electroplated onto the layerof nickel, the gold layer having a thickness of at least 50 microinches.The gold and nickel layers help to protect the ASTM-F15 steel materialof the metal plate 126 from damage due to environmental factors, such asthe corrosive characteristics of the lubricant gas which is disposedwithin the chamber 12 (FIG. 1) in the housing 11.

[0063] Next, with reference to block 237 in FIG. 10, the thickness ofthe nickel and gold layers is verified by an x-ray fluorescence (XRF)measurement, using techniques which are known in the art. In thedisclosed embodiment, this XRF measurement is carried out on a subset ofthe assemblies that each include a metal plate 126 with windows 106secured thereto. Then, at block 238, each of the glass windows 106 iscleaned on both sides. In the disclosed embodiment, this is carried outmanually, using a lint-free cloth and isopropyl alcohol.

[0064] As discussed above in association with FIGS. 1-3, the chromelayer 41 with the aperture 42 is optional. Consequently, at block 241, adecision is made as to whether the chrome layer 41 is to be provided inthe assembly which is currently being fabricated. If not, then the twosubsequent blocks at 242 and 243 are skipped. Otherwise, the processproceeds to block 242.

[0065] In block 242, a mask is used to apply a chrome layer to the lowerside of each of the glass windows 106. The mask is similar to the plateshown at 211 in FIGS. 13-14, except that the mask is made of metal andis significantly thinner than the plate 211. The mask is placed over thebottom side of the metal plate 126, so that the metal plate 126 iscovered and only the bottom surfaces of the glass windows 106 areexposed. A layer of chrome is then sputtered onto the bottom surface ofeach of the glass windows 106, with a thickness in the range of 700 Å to4,000 Å. The mask is then removed. Next, at block 243, a layer ofphotoresist is applied over the bottom surfaces of the metal plate 126and the glass windows 106. This photoresist is patterned using knowntechniques, and then the chrome layer is etched so as to create in thechrome layer on each of the glass windows 106 a rectangular aperture,which corresponds to the aperture shown at 42 in the chrome layer 41 ofFIGS. 1-2. The photoresist is then removed.

[0066] Next, at block 246 in FIG. 10, a mask is used to apply ananti-reflective coating to both sides of each of the glass windows 106.The mask used in block 146 is a thin metal mask which is physicallyequivalent to the metal mask discussed above in association with block242. Through use of the mask, the anti-reflective coating is applied toeach side surface of each window 106, but not to the gold-platedsurfaces of the metal plate 126.

[0067]FIG. 17 is a diagrammatic top view of the assembly as it appearsat this point in the fabrication process. The assembly of FIG. 17includes the metal plate 126, and the windows 106 secured in theopenings 127 of the plate 126. Reference numeral 251 denotes the chromelayer which is provided on and visible through one of the transparentwindows 106, and reference numeral 252 designates the rectangularaperture through the chrome layer 251. The anti-reflective coatings arepresent, but are not separately depicted in FIG. 17.

[0068] Next, at block 256 in FIG. 10, a not-illustrated sheet of plasticmaterial is temporarily applied to each side of the assembly shown inFIG. 17, for example in the form of a sheet of static cling plasticmaterial. The purpose of this plastic material is to protect the glasswindows 106 while pieces are cut from the plate 126. In particular,reference numeral 258 designates one of twenty rectangular broken lines,each of which represents a path along which a cut will be made throughbottom wall of a respective groove 136 in the metal. plate 126. Therectangular broken lines 258 in FIG. 17 each extend around a respectiveone of the glass windows and around an associated portion of the metalplate 126.

[0069] A precision cut is made along each of the broken lines 258, usinga fine-blanking procedure of a known type. Alternatively, the cuts alongthe broken lines 258 could be made using a not-illustrated diamond wheelsaw of a known type. After cuts have been made along each of the brokenlines 258, twenty sections of the assembly will have been cut from themetal plate 126, and each of these sections will be a lid which isidentical to the lid shown at 17 in FIGS. 1-2.

[0070] Next, with reference to block 261 in FIG. 10, the sheets ofstatic cling plastic are removed from both sides of each of the twentylids cut from the metal plate 126. Then, both sides of each window ineach of these lids is cleaned with a lint-free cloth and isopropylalcohol. In the rare event there is any residue which resists removal bythe isopropyl alcohol, acetone may optionally be used with a lint-freecloth to remove the residue. After cleaning, each lid is ready to beinstalled in an apparatus of the type shown at 10 in FIG. 1.

[0071] The present invention provides a number of technical advantages.One such technical advantage is that, because a number of steps duringthe fabrication process are each carried out so that a plurality ofoptical windows in a single assembly are processed simultaneously, theoverall cost of the resulting lids can be significantly reduced, by 25%or more.

[0072] One aspect of this is that the assembly can have a standard sizesuch as 7 inches by 7 inches, regardless of the precise number ofwindows being processed. In this regard, the 7 inch×7 inch assembly caninclude a large number of windows when the windows are relatively small,or a smaller number of windows when the windows are relatively large. Asa result, some specialized tooling may be needed for each configurationof the assembly, but certain other tooling can be standardized and usedfor all such assemblies having the standard size, regardless of thenumber of windows in any particular assembly. For example, when grindingand polishing the windows using double-disk grinding techniques, asingle set of standardized tooling compatible with the 7 inch×7 inchassembly size can be developed, and then used for all such assemblies,regardless of the specific number of windows in each assembly. Due tofactors such as the significant cost of specialized tooling,standardization of the tooling can help to significantly reduce theoverall costs of the resulting lids.

[0073] A further advantage is that separate lids are not cut from eachassembly until after almost all process steps have been completed, whichalso helps to effect a significant cost reduction. This is particularlytrue as to the steps of grinding and polishing the glass windows,applying and etching the optional chrome layers, and then applyinganti-reflective coatings.

[0074] Still another advantage is realized where a metal frame issubjected to a wet hydrogen process in order to remove impurities fromthe surface of the frame before it is oxidized and then fused to a glasswindow. The wet hydrogen process is significantly more effective atremoving impurities than pre-existing techniques. Due to the fact thatthe wet hydrogen process is particularly effective in removingimpurities, it results in a significant reduction in the formation ofgases and thus the formation of bubbles within the glass windows. Thisin turn effects a significant reduction in the number of parts that mustbe discarded as defective, which represents a significant increase inthe effective yield of the fabrication process, and thus a reduction inthe cost of each part.

[0075] Although one embodiment has been illustrated and described indetail, it will be understood that various substitutions and alterationsare possible without departing from the spirit and scope of the presentinvention, as defined by the following claims.

What is claimed is:
 1. An apparatus, comprising: a plate having aplurality of openings therethrough; and a plurality of windowscorresponding to the plurality of openings, the plurality of windowseach being transmissive to radiation having a predetermined wavelength,the plurality of windows each being secured to the plate in a mannerproviding an annular seal between an annular portion of the plurality ofwindows extending along a periphery thereof and an annular portion ofthe plate extending around the corresponding plurality of openings, theplurality of windows each having a processed surface, the plurality ofwindows each having an opaque layer with an aperture therethrough on onesurface.
 2. The apparatus of claim 1, wherein the plurality of windowsare thicker than the plate, the plurality of windows each being securedwithin the corresponding plurality of openings in the plate to projectoutwardly a small distance beyond the plate on each side thereof.
 3. Theapparatus of claim 1, wherein the plurality of windows each have aprocessed surface on each side thereof.
 4. The apparatus of claim 1,wherein the plurality of windows each have has a peripheral edge fuseddirectly to the material of the plate.
 5. The apparatus of claim 1,wherein the plate is a steel material and the plurality of windows eachbeing a borosilicate glass material.
 6. An apparatus, comprising: aplate having an opening therethrough; and a window corresponding to theopening, the window being transmissive to radiation having apredetermined wavelength, the window being secured to the plate in amanner providing an annular seal between an annular portion of thewindow extending along a periphery thereof and an annular portion of theplate extending around the openings, the window having a processedsurface, the window having an opaque layer with an aperture therethroughon one surface.
 7. The apparatus of claim 6, wherein the window isthicker than the plate, the window being secured within the opening inthe plate to project outwardly a small distance beyond the plate on eachside thereof.
 8. The apparatus of claim 6, wherein window has aprocessed surface on each side thereof.
 9. The apparatus of claim 6,wherein the window has a peripheral edge fused directly to the materialof the plate.
 10. The apparatus of claim 6, wherein the plate includes asteel material and the window includes a borosilicate glass material.11. The apparatus of claim 6, wherein the plate has a groove extendingentirely along its peripheral edge.
 12. The apparatus of claim 11,wherein the groove defines a flange having a generally uniform width andthickness along the peripheral edge of the plate.
 13. The apparatus ofclaim 6, wherein the window is transmissive to radiation in a range of420 nanometers to 700 nanometers.
 14. The apparatus of claim 6, whereinthe window is transmissive to radiation in a range centered at a centerwavelength of 545 nanometers.
 15. The apparatus of claim 14, wherein thewindow has an index of refraction of 1.47 to 1.50 at the centerwavelength.
 16. The apparatus of claim 6, wherein the opaque layerincludes chrome.
 17. The apparatus of claim 6, further comprising: ahousing surrounding a device in a chamber, the plate and window forminga lid for the housing and sealing the device in the chamber, the windowoperable to pass radiation to and from the device in the chamber. 18.The apparatus of claim 6, wherein the processed surface includes ananti-reflective material.